This application is based on Japanese Patent Application No. 11-68868 filed on Mar. 15, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an apparatus for examining a defect of a regularly disposed lattice patterns of a monolithic substrate and a method for examining the same.
2. Description of Related Art
Conventionally, for instance, the following method is known in this kind of an examining method. The examining method comprises capturing latticed patterns of a monolithic substrate, determining each of patterns from a captured image, and evaluating a shape of the determined pattern.
Incidentally, in a case of a monolithic substrate which has a lot of numbers of regularly disposed patterns, a higher magnification image is required for maintaining a measuring accuracy of a shape of the pattern sufficiently. Therefore, a lot of input processes of images are required because a field of a camera must be narrowed. As a result, there are disadvantages that the prior art brings an enlargement of a memory and an extension of a processing time.
A defect examining apparatus for addressing the above-mentioned problems is proposed in JP-A-6-242013. The apparatus captures an image of a wide area of an object having regularly repeated patterns, and processes image data which is captured. In this prior art, the image data is transformed into space frequency data by the Fourier transformation. A range of the space frequency data corresponding to the repetition of the patterns is masked. The masked space frequency data is processed by the Fourier reverse transformation to restore image data. The restored image data is provided for examining the defect of the repeated patterns. As a result, a ratio of a component corresponding to an irregularly formed defect to the masked data is increased relatively. The defect is indicated in an emphasized manner in the restored image data. Therefore, it is possible to detect the defect easily.
However, the following problems are appeared when the above-described method is applied for a monolithic substrate.
Specifically, the monolithic substrate has latticed patterns as repeated patterns which reach to an outer edge. The outer edge terminates the latticed patterns. Therefore, a defect can""t be sufficiently emphasized because an influence of an outer shape of the monolithic substrate remains, even if frequency components corresponding to regularly latticed patterns are removed. Therefore, it is difficult to accurately examine the defect based on the restored image data.
It is a further object of the present invention to provide a method and an apparatus to accurately examine a particular defect of the monolithic substrate of the lattice.
According to a first aspect of the present invention, captured image is processed by the Fourier transformation. Data corresponding to a particular component of frequency is removed from frequency data obtained by the Fourier transformation. The particular component includes a first component which is a frequency component depending on a regularity of the latticed patterns of the monolithic substrate. For instance, the first component is obtained on the basis of a perfect latticed-patterns having no defect. The particular component further includes a second component depending on an outer shape where the latticed patterns are terminated. For instance, a circle corresponding to an end shape of the monolithic substrate obtains the second component. As a result, it is obtained that data in which the particular components are declined. The data is processed by the Fourier reverse transformation. After that, the defect is detected based on the data after transformed by the Fourier reverse transformation. For instance, frequency data corresponding to a predetermined range is removed. The range is extended from a center which is the component corresponding to the regularly latticed-patterns. In the present invention, mean value of the image data is calculated at each lattice. The defect can be indicated when the mean value is out of a predetermined range.
Further, areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.